The present invention relates to a voltage measurement device that allows measuring capacity elements to accumulate terminal voltages for every block of a plurality of voltage sources (hundreds of storage batteries, fuel batteries, etc.) connected in series, through a first group of switches (semiconductor elements), thereby measuring accumulated voltages in the capacity elements through a second group of switches (semiconductor elements). More particularly, the invention relates to a calculating circuit for correcting errors of measured voltages due to parasitic capacitances inhering in the semiconductor elements forming the second group of switches.
From a viewpoint of environmental protection, there are known an electric car having a motor as a driving source for traveling the car and a hybrid vehicle having a motor and an engine as the driving source. It's often the case that hundreds of storage batteries or fuel batteries (which will be generally referred “batteries” below) connected in series are used for a power source for driving these motors. Recently, the need to measure terminal voltages of respective battery cells with high accuracy, which are connected in series and to which hundreds of voltage is impressed each, is increasing for purpose of monitoring the ever-changing charging state of the batteries during vehicle's traveling, the ever-changing discharging state, life-time of respective batteries, the presence of a malfunction and so on.
FIG. 1 shows a conventional voltage measurement system for measuring terminal voltages of such batteries with the use of charging/discharging of condensers.
The voltage measurement system in the figure comprises a voltage measuring part 2 connected to a battery 1, a voltage converting part 3 connected to an output side of the voltage measuring part 2 and a control part (not shown) for controlling the switching (ON/OFF) operation of the voltage measuring part 2 based on an output of the voltage converting part 3.
The battery 1 is composed of n (n: integral number more than 1) blocks connected in series (shown with only blocks N−1, N and N+1 in the figure). In each of the blocks, there are a plurality of battery cells connected in series, respectively forming voltage sources to be measured (shown with only voltage sources VCn−1, VCn, VCn+1 respectively corresponding to the blocks N−1, N and N+1 in the figure). This battery 1 outputs a high voltage, for example, 100 to 200 V.
The voltage measuring part 2 is composed of n voltage measurement circuits arranged for every block of the battery 1. The voltage measurement circuits include a first group of switches (switches P1, P2 corresponding to the block N in the shown example), condensers as the measuring capacity elements (illustrated by only condensers Cn−1, Cn, Cn+1 corresponding to the blocks N−1, N and N+1 in the shown example) and a second group of switches (switches N3, N4 corresponding to the block N in the shown example). Receiving a control signal from the control part, each voltage measurement circuit takes in a voltage from each block of the battery 1 through the first group of switches and holds the voltage in the corresponding condenser. Then, corresponding to a control signal from the control part, each voltage measurement circuit transmits the voltage held in the condenser to the voltage converting part 3 through the second group of switches.
The voltage converting part 3 is composed of, for example, an A/D converter. The voltage converting part 3 converts a voltage in the form of an analogue signal supplied from the voltage measuring part 2 to a digital signal and further transmits it to the control part.
The control part (not shown) supplies the voltage measuring part 2 with the control signals to control the operation of the part 2. In addition, the control part adds the digital signals transmitted from the voltage converting part 3 to calculate an overall voltage of the battery 1 and a voltage with respect to each block. The so-calculated voltages are used to monitor the charging state of the battery 1, the discharging state of the battery 1, a lifetime of the battery, the presence of malfunction, etc.
The voltage measurement system constructed above is adapted so as to measure the terminal voltages of the respective batteries (blocks) by first charging each terminal voltage of the plural batteries VCn−1, VCn, VCn+1 in series connection into the corresponding storage element (condenser) Cn−1, Cn, or Cn+1 through the switches P1, P2 in the first group SW1, secondly turning off them and subsequently connecting the storage element (condensers) Cn−1, Cn or Cn+1 with the voltage measuring unit (voltage converting part) V through the switches N3, N4 in the second group SW2.
The voltage measurement device, disclosed by Japanese Patent Application No. 2003-80406, utilizes the voltage measurement system like this. This related art has an object to provide a voltage measurement device which can measure terminal voltages of batteries quickly and accurately without an exclusive power source and which is compact at low price while being superior in noise resistance. For this purpose, the switches P1, P2 in the first group SW1 for controlling the charging operation are formed by Pch-MOSFETS (Metal-Oxide Semiconductor Field-Effect Transistors), while the switches N3, N4 in the second group SW2 for controlling the output operation are formed by Nch-MOSFETS (Metal-Oxide Semiconductor Field-Effect Transistors). With this constitution, the voltage measurement device is capable of measuring voltages of the batteries by first turning on the Pch-MOSFETS P1, P2 in the first group SW1 to charge a voltage from the battery VCn into an external condenser Cn, secondly turning off the Pch-MOSFETS P1, P2 in the first group SW1 and subsequently turning on the Nch-MOSFETS N3, N4 in the second group SW2 to output the voltage at an output terminal (S-terminal).